SIMULATION ON THE BREAKING OF αx MULTIKNOB ORTHOGONALITY IN THE PRESENCE OF GRADIENT AND COUPLING ERRORS AND EXPERIMENTAL INVESTIGATION*

S. Bai, J. Gao, IHEP, Beijing, China P. Bambade, LAL, Orsay, France G. White, SLAC, USA Abstract The ATF2 project is the final focus system prototype for ILC and CLIC linear collider projects, with a purpose to reach a 37nm vertical beam size at the interaction point. In beam tuning towards the goal beam size, the presence of a tilt of the IP Shintake monitor fringe pattern with respect to the x-y coordinate system of the beam can break the orthogonality in the main σ34 and σ32 waist corrections required to reduce the vertical beam size at IP. Concerning the method of doing αx scan and measuring the vertical beam size to diagnose the IPBSM fringe tilt or residual σ13, one thing should be studied is to check what could break the orthogonality of the αx knob other than σ13 and the IPBSM fringe tilt. In this paper, we report on the simulation study that check for the breaking of orthogonality of the αx knob in the presence of gradient and coupling errors; to what extent this breaking of orthogonality can go; and also calculate the IPBSM fringe tilt angle from experiment results.